Yup, BaDa was the lead singer in SES. I'm not sure if she's in Summer Vacation though because I haven't seen it yet. Short history...

SES (Standing for the names Sea, Eugene, and Shoo) was the greatest female KPop group of all-time. When they debuted on November 28th, 1997 with 'I'm Your Girl', they instantly shot to number one status because this was the first girl-group that dominated in a time where boybands were the 'thing' in the music industry in Korea. They constantly charted out number one singles and albums and paved the road for other top girl-groups Baby VOX (Short for 'Voice Of eXpression and Fin.K.L. (FINe Killing Liberty). After some fans were startled of the absence of BaDa and Eugene in SM Towns Winter Album in 2002 and refusals to sing 'S. II. S.' (Soul To Soul) on their 5.5 album (They had recently shattered their cute image with a new mature image, like what BoA* is starting to do- On the 5th album they were in a somewhat t.A.T.u. like schoolgirl-outfit pose), it was announced that SES was in fact breaking up on December 25th, 2002. Both BaDa and Eugene have released their albums (She changed her name from 'Sea' to 'Bada', which actually means 'Sea' in Korean), and were quickly compared to Fin.K.L.'s singers who were also releasing solo albums but were staying together- Eugene released her album at the time Ock Ju Hyun released hers, and BaDa released her album a few weeks after HyoRi released hers. She also signed the richest female contract at $1.7 million (3 albums and a specials album), and also signed a record deal with another company. The main comparison was between HyoRi and BaDa though because they were both the lead singers of the groups. While BaDa was thought to sing ballads and R&B, she released what she called 'her own style' of music.

Although both were expected to do somewhat good, I think HyoRi is doing much better mainly because of her title song '10 Minutes' that made her become known as the 'Lee HyoRi Syndrome'.